Light-emitting diodes are quickly becoming a popular light source for indoor task and area lighting, providing high energy efficiency and long life expectancy. One drawback of the light-emitting diode is that for a typical installation of an LED-based luminaire mounted on a ceiling and directed straight down, the LEDs only provide light through a range of 120°, failing to illuminate the first 30° from the ceiling.
For example, the attached FIG. 1 illustrates a prior art installation 100 of a single LED 110 mounted on a ceiling 120 and pointed straight down, in which the LED 110 only provides light through a range of 120°, failing to illuminate the first 30° from the ceiling 120.
FIG. 2A illustrates another prior art installation 200 of a first, second, and third band of LEDs 210, 220, and 230, respectively. Such a prior art design may be seen, for example, in FIG. 14 of U.S. Pat. No. 8,750,671, granted to Kelly et al. on Jun. 10, 2014. In this configuration, each of the three bands of LEDs 210, 220, and 230 follows an arc, with the LEDs oriented normal to the arc. Thus, the center LED is aimed straight down, or nearly straight down, and the other LEDs are directed or aimed at an angle to the floor. Note that when this description mentions the orientation of an LED, it is with regard to the aimpoint of the output light.
As may be seen in FIG. 2B, if one assumes that an LED has a typical light distribution of 120°, then obtaining 180° coverage along one axis can be obtained by distributing a plurality of LEDs into a 60° arc 250, i.e., with the LED 260 at one end of each arc aimed at 30° above the floor in one direction, e.g., north, and with the LED 270 at the other end of each arc aimed at 30° above the floor in the opposite direction, e.g., south.
While this prior art design is an improvement over the problem presented by the construction where all LEDs are simply aimed straight down and directly at the floor below, e.g., as illustrated in FIG. 1, it still only provides a 180° lighting distribution along one axis. That is, as discussed above, each of the three bands of LEDs 210, 220, and 230 follows an arc. The apexes of each arcuate LED band 210, 220, and 230 are placed along horizontal line 240, being an axis perpendicular to the length of arcuate LED bands 210, 220, and 230. The center LEDs of LED bands 210, 220, and 230 are aimed straight down. Thus, the 180° distribution will only be present in the axis parallel to the length of arcuate LED bands 210, 220, 230, i.e., perpendicular to axis 240. Thus, in the example given, the 180° distribution would be present along the north-south axis, but the east-west axis would still only provide a 120° distribution.
What is required is an improved luminaire based on LEDs that provides illumination through a greater angular range, including up to 180°.